Process of preparing acetic acid from acetaldehyde



L 1 'Iiheypresent invention relates to PatenteclMay 14, 1935 rnooi sslon nREPARmG AoETIdAom FROM ACETALDEHYDE Walter, I inapsabk,

near Cologne-on-the-Rhine, Germany,xa"s'signors to 'Aktiengcsellschaft ifur Stickstoffdunger,

- Knapsack,

many

near; Cologne-on-the-Rhine, Ger- No Drawing. Application September 30, 1933,

a new process oftpreparing acetic. acid from acetaldehyde' We haveiound that the well'v-kno'wn process qfia epa ring acetic; acid from. acetaldehyde by causing oxygen or oxygen containing gases. to react;upon.acetaldehyde dissolved in acetic acid or-,;another-, solventtor acet'aldehyde and acetic acid; can be; considerably :improved as tov a better yiel nd a better reactionv'elocity if the reaction is performed-in the presence. of ozone and atem peratnre above C. l H V l- As is -stated above the-reaction temperature mustbe kept above-0 C., and it is pointed out that an exact upper limit cannot be given. However, the temperatureis. preferably not allowed 1 to rise over the boiling-point of acetic acid which obviously dependsfon.the working pressure. The acetic acid obtained according to our. present+invention, is distinguishedby its highdegree cat-purity; it does not leave behindany solid residuesif evaporated and cam-therefore, directly be -used for most purposes without the necessity of purifyin gor rectifying it.. The amount of percompounds formed during .thereaction is so small that .nodanger of explosions will arise.

Moreover-, lpercompounds; 'if formed, are convented-into acetic acid a by the action of .the acetaldehyde withoutgiving rise. to the formation of a considerable amount of. gaseous decomposi t o products.

.The reaction can: beperformed in. the presence of acetic acid aswell as in: any other. solvent" for acetaldehyde and acetic acid. l which does not chemicallyreact with the oxidizing gases. orwith acetic acid andacetaldehyde.

he reaction-is performed in the presence of acetic acid as. solvent-care must be taken that acetic acidis continuously removed from the reaction. vesselin the same degree as it is formed.

\ I .T he acetict acid thus removed is freed from acetaldehyde dissolved therein which upon con- 3 densation-is ledback-into the reaction vessel together with volatile liquids if solvents. other than acetic acid and'tof alower boiling. point than acetictacid arel used.

The-oxidizing gases whichare preferably finedistributed by means of. sieve plates, porous I filters or iri any} other. way can simultaneously serve for-thoroughly mixing the reaction liquid. The .mixingofgthe liquid can likewise be. effected iby mechanical means.

The removal of the heat of reaction and maintenance of the desired temperatureicanfbe eflected iingknown manner by external or internal cooling devices, ifl desired, by subjecting entering thebottom of the chamber in a finely ingin technical scale, one will .uselthe ozone of a solvent, the boiling point of which coincides ,5

can be used as "such a solvent.

The reaction mixture can be caused to circulatesolely by the-action offlthe oxidizing gases with the said temperature. I Acetaldehyde itself divided form. In this methodof performingthe reaction the circulating liquid 'le'aves'the reaction vessel by way of alnoverfiow, enters a cooler and is led back into, the bottom part of theichamher. [The necessary flow of the liquid is eilected may by 'the Idifier'ence between the specific Weight-of the liquid in the reactionchamb'er and that'ofthe'liquid inthe cooler, the lowerspecific weight of "the formerj.'being due to the. higher temperature. and to the presence "of the finely di- 2 vided oxidizingqgases. "Thefl ow of'liquid can be regulated: in know'n mannergarid can, of course, be efiected likewise byanyiother mechanical meansf" v 1 i l The reaction. liquid i canl be 1 prevented *irom flowing back' mm the pipe for the oxidizing gases by a check valve or asimilar device. The ozone maybeproduced directly in the oxidizing gases or it may be previously. prepared and ledintothe chamber diss'olvd in acetic. acid, if desired, simultaneously with theoizidizinggases. N -'I'heamount. of the ozone to be u'sed foreffecting the best activation of the-oxygen depends on the working conditions. Howevenlwhen workin an amountqconsiderably smaller than the optimumamount. 8 p

. The ozone is completely consumed in the course of-the reaction and it is evident therefrom thatif air is used. as oxidizing gas, there is obtainedas waste producta gas which upon eliminational small traces .ofsolvent, of acetic acid andacetaldehyde, consists substantially of mm); gen and we wish to point outthat our present invention concerns likewise a process of preparing pure nitrogen. "In order .to cause the separation of the small amounts of the reaction componentsand the solvent whichare carried along, the nitrogen may be used for driving a pressed gas pump known as a mammoth pumpiand thus :for conveying liquids for washing out the nitrogen. i i

Although the chief factor of .ourpresent inventionresides in the use. of ozone, we Wish to point out that, nevertheless, the well-known solid catalysts, such as compounds of manganese uranium, lead, iron, chromium, vanadium or combinations thereof can be used simultaneously with the use of ozone. It is known that the said solid catalysts effect a considerable increase of the speed of reaction and it is a surprising fact that the reaction velocity is still more increased by the use of ozone according to our present invention. Moreover, the yield of acetic acid, calculated upon the acetaldehyde, becomes nearly quantitative (about 99.6%) if ozone is used as a catalyst. Moreover, the formation of the higher degree of valence of the solid catalysts which is decisive for the absorption of oxygen and the setting in of the reaction is considerably accelerated by the presence of ozone.

Our new process can be performed in any suitable apparatus. Reaction towers as well as columns filled with fillers, shaking apparatus and stirring apparatus can be used. The apparatus can be subdivided into several sections. The process can be carried out in a direct current, i. e, by causing the solvent, the acetic acid and the acetaldehyde to enter the reaction chamber at the bottom, or in counter current. The acetaldehyde can be introduced either in a pure state, or dissolved in a suitable solvent.

The following examples serve to illustrate the invention, but they are not intended to limit it thereto, the parts being by weight. It is to be understood that only small changes are necessary for performing the process in a discontinuous manner.

(1) A tower provided with a sieve plate at the bottom is filled with 3000 parts of crude acetic acid containing 60 parts of acetaldehyde, the temperature being about 58 C. Through the sieve plate there are introduced every hour about I 236 parts of ozonized air with an ozone content of 0.5 per cent by weight,'the pressure being about 3 to 6 atmospheres. The liquid content of the tower flows over into a cooler and the acetic acid which has passed the tower is loaded with 150 parts of acetaldehyde every hour and reintroduced into the tower at a place above the sieve plate. The circulation of the-reaction liquid is regulated in such a manner that the initial temperature of about 58 C. in the tower is maintained. A second overflow is arranged just above the first overflow which serves for removing continuously acetic acid in the same degree as it is formed in the tower. The acetic acid removed from the tower is led into a heated vessel provided with a column wherein it is freed from small traces of acetaldehyde which is reconducted into the acetaldehyde pipe. The acetic acid thus obtained is as bright as water and has a strength of about 99.0%.

When strictly observing the above conditions, there escapes at the top part of the tower a waste gas consisting substantially of nitrogen with small traces of acetic acid and acetaldehyde, which are removed by washing the gases in a trickling tower with cold acetic acid. The acetic acid used for this purpose is derived from the cooler for the circulating acetic acid and after having, passed the trickling tower and having been loaded with acetaldehyde, it is led over a siphon to a reservoir, wherefrom it is reconducted into the process. The last traces of acetaldehyde contained in the nitrogen are condensed in a cooler and led back into the reaction tower. The nitrogen thus obtained contains only very small traces of oxygen and no ozone. The yield of acetic acid is about 99%.

(2) An apparatus similar to that described in Example 1 is used, the trickling tower being dispensed with. The tower which is likewise provided with a sieve plate at the bottom is filled with 3000 parts of crude acetic acid of a temperature of about 50 C. which contains 60 parts of acetaldehyde. The overflow at the top part of the tower leads over a cooler to a pump which introduces continuously 180 parts of acetaldehyde every hour and effects a thorough mixing of the acetaldehyde with the acetic acid. This mixture enters the lower part of the tower just above the sieve plate where it meets every hour 65.5 parts of ozonized oxygen of an ozone content of 2.7% by weight. In order to ensure a complete absorption of the oxygen and ozone without the necessity of enlarging the tower it is advisable to work at a pressure of about 2 to 4 atmospheres. The circulation of acetic acid is controlled so that the temperature in the tower is maintained at about 50 C. Acetic acid is continuously removed from the system and purified as described in Example 1. There is obtained a yield of acetic acid of about 99%, the per cent content of acetic acid being 99%.

Above the tower there is a cooler for condensing the last traces of acetaldehyde which are reconducted into the system. There is obtained only a small amount'of waste gases consisting of carbon dioxide and carbon monoxide.

(3) In an apparatus similar to that described in Example 2 there is used instead of the reaction tower a vessel which is provided with a wellacting rapid-stirrer and in the lower part with a finely perforated plate for distributing the oxidizing gases. Besides, the vessel is provided with sockets for the circulation of the acetic acid, for measuring the temperatures and possesses a gas delivery tube with a cooler. In the reaction vessel, there are introduced 3000 parts of acetic acid in which 3 parts of manganese acetate are dissolved and the solution is heated to 40 C. The acetic acid is caused to circulate over a cooler by means of a pump. After the circulating acetic acid has left the cooler, 150 parts of acetaldehyde and 0.2 part of manganese acetate in concentrated aqueous or acetic acid solution are continuously added per hour so that by means of the pump the circulating acetic acid is thoroughly mixed with the said substances added. 54.5 parts of ozonized oxygen which contain 1 g. of ozone per 100 g. of oxygen enter continuously per hour through the perforated plate into the reaction vessel, and after a very short time the reaction liquid begins to assume a brown coloration. The latter which is caused by the formation of manganese compounds of a high valence deepens very rapidly pari passu with the absorption of the oxidizing gases. The circulation of the liquid is regulated so that the temperature in the reaction vessel is 40 C. The traces of acetaldehyde which possibly remain in the dissolved condition in the acetic acid flowing off into the heating still may be recovered and reconducted into the reaction vessel. If the reaction liquid is well stirred and sufficiently pure oxygen is used, the oxidizing gases are completely consumed, so that practically no waste gases are produced.

The oxidation takes place under usual atmospheric pressure. The yield amounts to 99.6%, acetic acid of about 99 per cent strength being obtained.

We claim:

1. The process which comprises reacting with oxygen and ozone upon acetaldehyde in the presence of a solvent for acetic acid and acct-aldehyde at a temperature above 0 C.

2. The process which comprises reacting with oxygen and ozone upon acetaldehyde dissolved in acetic acid at a temperature above 0 C. 1

3. The process which comprises reacting with oxygen and ozone upon acetaldehyde in the presence of a solvent for acetic acid and acetaldehyde at a temperature above 0 C., while adding a solid catalyst known to promote the oxidation aldehyde.

4. The process which comprises reacting with oxygen and ozone upon acetaldehyde dissolved in acetic acid at a temperature above 0 C., while adding a solid catalyst known to promote the oxidation of acetaldehyde.

5. The process which comprises reacting with oxygen and ozone upon acetaldehyde in the presof acetence of a solvent for acetic acid and acetaldehyde at a temperature above 0 0., while applying pressure. a a a 6. The process which comprises reacting with oxygen and ozone upon acetaldehyde in the presence of a solvent for acetic acid and acetaldehyde at a temperature above 0 C., while causing the reaction liquid to circulate so as to remove the heat of reaction. 3

7. The process which comprises reacting with air and ozone upon acetaldehyde in the presence of a solvent for acetic acid and acetaldehyde at a temperature above 0 C., while causing the oxygen content of the air to be completely absorbed so as to obtain a waste gas consisting substantially of nitrogen.

KARL WEIBEZAHN. FELIX WALTER. 

